\begin{tikzpicture}[>=Stealth, scale=0.5,
    every node/.style={fill=white, inner sep=1pt},
]
    \draw [->] (-6, 0) -- (6, 0) node[below=0.2em] {$x$};
    \draw [->] (0, -6) -- (0, 6) node[left=0.2em] {$y$};
    \draw (0, 0) node [below right=0.3em] {\small $O$};
    \foreach \x in {-5, ..., 5} {
        \draw (\x, 0) -- (\x, 0.2);
    }
    \foreach \y in {-5, ..., 5} {
        \draw (0, \y) -- (0.2, \y);
    }

    \draw[domain=-2.6:2.6, samples=10] plot (\x, {2*\x}) node [above] {$y = 2x$};
    \draw[domain=-4.0:4.0, samples=10] plot (\x, {\x})   node [above] {$y = x$};
    \draw[domain=-5.0:5.0, samples=10] plot (\x, {\x/2}) node [above] {$y = \frac{1}{2}x$};
    \draw [fill=black] (0, 0) circle(0.1);
    \draw [fill=black] (1, 2)   circle(0.1) node [left=3pt] {\small $A$};
    \draw [fill=black] (1, 1)   circle(0.1) node [above right=3pt] {\small $B$};
    \draw [fill=black] (1, 0.5) circle(0.1) node [right=3pt] {\small $C$};
\end{tikzpicture}

